This application claims the priority of 198 33 304.8-21, filed Jul. 24, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an apparatus for actuating a brake of vehicles, and more particularly, to a brake actuation apparatus having an electric motor and a coupling element which is coupled in terms of movement with the said electric motor, is linearly movable, can be connected to a brake tensioning mechanism and is transferred by the energized electric motor out of a braking position into a release position. An electrically actuated blocking device provides block on movement of the coupling element, at least in the release position. A spring energy store is movement coupled with the coupling element such that, in the release position of the coupling element, it assumes a storage position storing spring energy, and, when the block on movement is overridden, transfers the coupling element into the braking position by the released spring energy.
Apparatuses which, for actuating a brake, include an electric motor, a gear mechanism and a spring energy store are described in DE 25 46 470 A1; DE 27 10 585 C2; and DE 44 03 719 C1. In a release position of the known apparatus, not actuating the brake, the pre-loaded spring of the spring energy store assumes a position in which it stores spring energy. To maintain this release position, an electrically actuatable blocking device for the motor drive shaft or the gear mechanism is provided or the electric motor is supplied with a low holding voltage for its blocking. These known apparatuses have a disadvantage in that the spring energy store automatically relaxes if there is a power failure and the apparatus is consequently transferred into a braking position, thereby actuating the brake. This automatic braking operation may lead to considerable disturbances and safety risks in the operation of the vehicle.
A further apparatus for electronic brake actuation, disclosed in DE 30 48 766 A1, dispenses with a spring energy store for reaching the braking position. The braking position is achieved by a corresponding loading of the electric motor. In the event of a power failure, a shaft stub of the motor drive shaft must then be turned manually by a tool if braking is to be carried out. The driver finds this to be inconvenient. If this apparatus is used in a parking brake, a power failure makes it first necessary for the driver to leave a parked vehicle if he wishes to secure the vehicle by the parking brake. This necessity is either not possible at all, in particular on inclined carriageway surfaces, or entails considerable safety risks (risk of the vehicle rolling away) both to the driver and possibly other persons and to the vehicle.